Research

Ongoing projects in the laboratory address several questions pertinent to the cell biology of neutrophil-mediated responses during inflammation and host response to infection. As the dominant cellular component in “pus”, neutrophils respond immediately to infectious challenges and serve as the sentinel of the inflammatory response. We have a longstanding interest in two important aspects of the neutrophil response, namely the NADPH-dependent oxidase and the granule hemeprotein myeloperoxidase (MPO), and have active projects examining various aspects of each of these important elements of acute inflammation. Studies on the NADPH-dependent oxidase are directed at understanding the molecular basis for the temporal and spatial control of oxidant production in the phagosome, the subcellular compartment in which the ingested microbe is trapped. More recently our studies have extended to include the cell biology of related NADPH oxidase systems in non phagocytic cells, where oxidant generation serves purposes other than host defense. Studies related to our interest in MPO include characterization of MPO biosynthesis and the identification of various genotypes of inherited MPO deficiency. Studies on MPO biosynthesis include characterization of the role of molecular chaperones calreticulin and calnexin in the early steps of MPO processing, as well as assessment of the various "quality control" mechanisms operating in the endoplasmic reticulum of myeloid precursors. In addition, studies are ongoing to define the mechanism by which heme is incorporated into MPO. The impact of heme insertion on the subsequent proteolytic processing and intracellular targeting of MPO to the lysosome is also under study. Studies of hereditary MPO deficiency also include identification of the genotype underlying the specific phenotype and then characterization of the impact of that mutation on the synthesis of MPO. For these studies we used transfected HEK cells to express mutant MPO cDNA and characterize the biosynthesis. Our findings from such analysis complement well those derived from studies of MPO biosynthesis in established myeloid cell lines. Lastly, these two lines of investigation converge in our ongoing work on how neutrophils kill staphylococci and how the recently emerging community acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) survives within neutrophils. CA-MRSA have become an enormous clinical problem in the community in the past 5-7 years, and the biologic basis for the organism’s enhanced virulence is not understood, but likely linked to it ability to endure, evade, and subvert neutrophil killing.